As far as size, 5 inches max. Several wrasses do grow to 10-12 inches, but not the yellow.
The yellow wrasse will target anything that is very small and can fit into it's mouth. That includes pods, very small bristle worms, very tiny snails. The key words are very small. It will not mess with a cleaner, pepperment, or fire shrimp. Anything of size the yellow will stay away. They are very peaceful. Hard to say on small hitchhiker stars. If they are really tiny I suppose it's possible, but if they have any size to them they would be okay.
Color, personality, activity make this a great choice. Plus, they don't cost a lot.